This invention relates generally to rate sensing systems, and more particularly, to gyro motors and start up sequences for gyro motors.
During a startup phase of certain known gyro motors, a transient signal such as a pulse or a noise burst is used to excite the very lightly damped motor structure of the gyro motor. The motor responds with a very small and slowly decaying sinusoidal pick-off signal. This pick-off signal is typically applied to a gain circuit, which applies a large gain to the pick-off signal in an attempt to provide a constant amplitude sinusoidal signal to a motor control loop. The motor control loop tries to acquire the sinusoid signal with a phase-locked loop (PLL), which provides a motor drive signal at an appropriate frequency, magnitude, and phase. When the PLL xe2x80x9ccatchesxe2x80x9d and the correct motor drive signal is applied, the amplitude of the motor pick-off signal suddenly increases by orders of magnitude, and can overwhelm an analog-to-digital converter (ADC) in the motor control loop. Therefore, in known motor control loops, the large variations in the pick-off signal prevent a constant amplitude sinusoidal signal from being generated.
In one aspect, an apparatus for controlling an amplitude of a signal generated from a digitized sinusoid signal of rapidly and widely varying amplitude is provided. The apparatus comprises a two stage gain adjuster which produces a gain adjusted signal and a phase shifter which converts the gain adjusted signal into two gain adjusted output signals separated in phase by 90 degrees. The apparatus further comprises a power estimation unit to estimate the power of the gain adjusted signal and an adjusting unit to adjust a gain of the gain adjuster according to a power estimate from said power estimation unit and a desired output signal power.
In another aspect, a method for controlling the amplitude of a signal generated from a digitized sinusoid signal of rapidly and widely varying amplitude is provided. The method comprises producing a gain adjusted signal from the sinusoid signal utilizing a two stage gain adjuster and converting the gain adjusted signal into two gain adjusted output signals separated in phase by 90 degrees utilizing a phase shifter. The method also comprises estimating the power of the gain adjusted signal and adjusting the gain of the gain adjuster according to the estimated power and a desired output signal power.
In yet another aspect, a control circuit for a gyro is provided. The control circuit comprises a phase-locked loop configured to supply a motor control signal, and a motor signal conditioning circuit which converts the motor control signal to an analog motor drive signal. The phase-locked loop further comprises an analog-to-digital converter configured to receive a gyro pick-off signal, an automatic gain control circuit to provide amplitude control to an output of the analog-to-digital converter, and a numerically controlled digital dual frequency oscillator.